An executive says Alliant Energy's Iowa subsidiary Interstate Power & Light Co. will file next month for a rate increase that would raise the average customer's bill by more than 10 percent.

Joel Schmidt is a vice president for Alliant, and he told the Dubuque Telegraph Herald that the proposed base rate increase would be the first sought since 2010 and wouldn't take full effect until early next year. Higher rates will be sought for residential and commercial customers.

He says the filings to the Iowa Utilities Board are scheduled for April 3.

Schmidt says Alliant is seeking the increase primarily to modernize and maintain its grid and provide money for investments in clean energy.